Colloid solution of metal nanoparticles, metal-polymer nanocomposites and methods for preparation thereof

ABSTRACT

A metal nanoparticle colloid solution, metal-polymer nanocomposites, and methods for preparing the same are provided. The metal nanoparticle colloid solution and the metal-polymer nanocomposites can be prepared with a variety of polymeric stabilizers and have uniform particle diameter and shape. The metal nanoparticle colloid solution and the metal-polymer nanocomposites have wide applications, for example, as an antibacterial agent, a sterilizer, a conductive adhesiv, conductive ink or an electromagnetic wave shielder for an image display.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a colloid solution of metalnanoparticles, metal-polymer nanocomposites, and methods for preparingthe same, and more particularly, to a metal colloid solution andmetal-polymer nanocomposites prepared using a variety of polymericstabilizers and having a uniform particle diameter, and methods forpreparing the same.

2. Description of the Related Art

Recently, a method for preparing a colloidal dispersion of silvernanoparticles using gamma rays and appropriate stabilizers, such aspolyvinyl alcohol and sodium dodecyl sulfate (SDS) was disclosed (Nature1985, 317, 344; Materials Letters 1993, 17, 314). The preparation methodusing gamma rays was reported to provide uniform diameter distributionof the silver nanoparticles. The metal nanoparticles prepared by thosemethods were known to have a size of from about 8 nm to tens ofnanometers from the outstanding research reports. However, the metalnanoparticles are prepared by these methods not so desirable in terms ofparticle diameter and shape uniformity.

It is important to obtain pure silver particles having a uniform shapewithin a narrow distribution range of particle diameters for industrialapplications. For example, ultrafine silver particles are essentialmaterials in the electronics applications, for example, for conductiveink and paste and adhesive applied in the manufacture of a variety ofelectronic parts.

As described above, there is a need for a new method for preparing metalnanoparticles having a uniform size and shape. In addition, gooddispersion stability for preventing agglomeration of metal nanoparticlesin a dispersion medium is another consideration for industrialapplications. For diversified industrial applications, miscibility witha variety of organic solvents, plasticizers, and resins is required toprepare a metal colloid solution in a non-aqueous medium.

A variety of methods for preparing a solid phase of polymer-metalnanocomposites were suggested (Polym. Composites 1996, 7, 125; J. Appl.Polym. Sci. 1995, 55, 371; J. Appl. Polym. Sci. 1996, 60, 323). Thesemethods involve two steps: (1) polymerization of monomer particles and(2) reduction of metal ions in a polymerized medium. However, theseparate polymerization and reduction processes cause non-uniform sizedistribution of the metal nanoparticles in the polymerized medium.

To solve this problem, a method for preparing silver-polymernanocomposites using gamma rays was developed (Chem. Commun. 1997,1081). In the method, a silver salt is dissolved in water, mixed withacrylic amide as a water-soluble monomer, and subjected to gamma-raysirradiation to prepare the silver-polymer nanocomposites. Here,reduction of silver ions coincides with polymerization of the monomer,so that the metal nanoparticles are comparatively uniformly dispersed inthe polymerized medium.

However, this method also cannot be applied when using a variety ofwater-insoluble monomers. To overcome the limitation encountered whenusing an aqueous medium, the preparation of silver-polymernanocomposites from a water-in-oil (W/O) emulsion was reported (Chem.Commun. 1998, 941), wherein toluene was used for the oil phase.

According to the method, since a variety of water-insoluble monomers canbe applied, various kinds of metal-polymer nanoparticles can beprepared. However, the use of excess toluene for the oily medium, up toabout 5 times the amount of water, causes environmental concerns. Inaddition, a safe working environment is not guaranteed due to a highrisk of explosion in its preparation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide acolloid solution of metal nanoparticles having a uniform particlecharacters and a method for preparing the same.

It is another object of the present invention to provide metal-polymernanocomposites having a uniform particle characters and a method forpreparing the same.

In one aspect, the present invention provides a method for preparing ametal nanoparticle colloid solution, comprising: dissolving a metal saltand a water-soluble polymer in water, a non-aqueous solvent, or asolvent mixture of water and a non-aqueous solvent; purging a reactioncontainer containing the solution with nitrogen or argon gas; andradiating radioactive rays onto the solution.

In the preparation method, the water-soluble polymer includes polyvinylpyrrolidone, a copolymer having vinyl pyrrolidone as a firstpolymerization unit, and a fatty acid-substituted or unsubstitutedpolyoxyethylene. The copolymer having vinyl pyrrolidone as the firstpolymerization unit includes (1-vinyl pyrrolidone)-acrylic acidcopolymer, (1-vinyl pyrrolidone)-vinyl acetic acid copolymer, (1-vinylpyrrolidone)-styrene copolymer, and (1-vinyl pyrrolidone)-vinyl alcoholcopolymer. The fatty acid-substituted polyoxyethylene includespolyoxyethylene stearate and polyoxyethylene palmitate.

In another aspect, the present invention provides a metal nanoparticlecolloid solution prepared by the preparation method described above.

In another aspect, the present invention provides a method for preparingmetal-polymer nanocomposites, comprising: dissolving a metal salt and apolymeric stabilizer in a solvent mixture of water and a non-aqueoussolvent; purging a reaction container containing the solution withnitrogen or argon gas; and radiating radioactive rays onto the solutionto obtain precipitates.

In the preparation method of the metal-polymer nanocomposites, thepolymeric stabilizer is at least one polymer selected from the groupconsisting of polyethylene, polyacrylonitrile, poly(methyl(meth)acrylate), polyurethane, polyacrylamide, and polyethylene glycol.

According to the present invention, the colloid solution of metalnanoparticles and the metal-polymer nanocomposites have favorablestability, a uniform shape, and a small diameter within a narrowdistribution range, so that the colloid solution of metal nanoparticlesand the metal-polymer nanocomposites have wide, effective applications,for example, as an antibacterial agent, a deodorizing agent, aconductive adhesive, conductive ink, and a electromagnetic wave shielderfor an image display.

The formation of the silver nanoparticles will be described in greaterdetail. Electrons are generated in a solvent by gamma-rays irradiationand reduce silver ions in a solution. Reduced silver atoms agglomerateto form a silver cluster and become larger. In this case, when anappropriate polymeric stabilizer is added, the agglomeration of thesilver atoms can be prevented to result in nano-sized silver particles.Polymeric stabilizers stabilize the nanoparticles in a colloid statethrough steric repulsion as well as prevent the silver clustering. Thegamma-rays irradiation produces radicals as well as the electrons in thesolvent. To remove the radicals, a scavenger, such as alcohol, is used.Oxygen present in the solution is removed by nitrogen or argon purgingbefore the gamma-rays irradiation, to prevent side reactions by theoxygen.

To prepare the colloid solution of metal nanoparticles according to thepresent invention, any metal salt capable of forming a generalnanoparticle colloid solution can be used without limitations. However,in terms of conductivity and economical reasons, a salt of at least onemetal selected from the group consisting of silver, copper, nickel,palladium, and platinum is preferable, with the silver salt being morepreferable.

The metal salt is, for example, nitrate, sulfate, hydrochloride,perchlorate, or acetate. According to the present invention, a silversalt, such as AgNO₃, AgClO₄, Ag₂SO₄, or CH₃COOAg is more preferred.These silver salts are well dissolved in water and thus form an aqueouscolloid of silver nanoparticles.

In the preparation of the colloid solution of metal nanoparticlesaccording to the present invention, a water-soluble polymer, preferably,having a weight average molecular weight of 2,000-2,000,000, is used asa stabilizer for improving dispersion of the metal nanoparticles.Suitable stabilizers include, for example, polyvinyl pyrrolidone, acopolymer including vinyl pyrrolidone as a first polymerization unit,and a fatty acid-substituted or unsubstituted polyoxyethylene.

The copolymer including vinyl pyrrolidone as a first polymerization unitmay further include an acrylic acid, styrene, vinyl acetate, or vinylalcohol as a second polymerization unit. Examples of the copolymerinclude (1-vinyl pyrrolidone)-acrylic acid copolymer and (1-vinylpyrrolidone)-vinyl acetic acid copolymer. The copolymer includes thefirst and second polymerization units in a weight ratio of 1:99-99:1,and preferably, 20:80-80:20. Preferably, the (1-vinylpyrrolidone)-acrylic acid copolymer includes a 1-vinyl pyrrolidonerepeating unit and an acrylic acid repeating unit in a weight ratio of75:25. Preferably, the (1-vinyl pyrrolidone)-vinyl acetic acid copolymerincludes a 1-vinyl pyrrolidone repeating unit and a vinyl acetic acidrepeating unit in a weight ratio of 57:43.

Regarding the fatty acid-substituted polyoxyethylene, which is awater-soluble polymer used as the stabilizer, the fatty acid is palmiticacid, oleic acid, linoleic acid, or stearic acid, with the stearic acidbeing more preferred.

Any solvent capable of dissolving the water-soluble polymer and metalsalt therein can be used without limitations. For example, water, anon-aqueous solvent, or a mixture of these solvents can be used.Suitable non-aqueous solvents include alcoholic solvents, and typically,isopropyl alcohol, methanol, ethanol, ethylene glycol, or a mixtureincluding at least two of the forgoing solvents.

The non-aqueous solvents also act as a scavenger for removing radicalsduring gamma-rays radiation as well as act as a solvent for the metalsalt and water-soluble polymer.

According to the present invention, the water-soluble polymer is used inan amount of 0.1-10 parts by weight based on 100 parts of the solvent byweight. If the water-soluble polymer is used in an amount of less than0.1 parts by weight, it is difficult to provide the effect of thestabilizer. If the water-soluble polymer is used in an amount of greaterthan 10 parts by weight, the particle size undesirably increases.

According to the present invention, the metal salt is used in an amountof 0.01-5 parts by weight based on 100 parts of the solvent by weight.If the metal salt is used in an amount of less than 0.01 parts byweight, it is difficult to provide the effect of the metal salt. If themetal salt is used in an amount of greater than 5 parts by weight, theparticle size increases, or the particles slightly precipitate.

In the preparation of the colloid solution of metal nanoparticlesaccording to the present invention, a water-soluble polymer and a metalsalt are dissolved in a solvent. A reaction container containing thesolution is purged with nitrogen (N₂) or argon (Ar) gas for 10 minutesto 10 hours and tightly sealed.

Next, the resultant product is irradiated with radioactive rays, andpreferably, gamma rays, to a radiation dosage of 10-50 KGy. As a result,the colloid solution of metal nanoparticles having a much smallerparticle diameter of about 1-5 nm than those prepared by conventionalmethods, within a narrow distribution of particle diameters, isobtained.

In the colloid solution of metal nanoparticles prepared by the methodaccording to the present invention, a post-process of diluting thesource solution and ultrasonic treatment may be performed to decomposethe metal nanoparticles further into much smaller metal particles. Thepost-process supports the fact that the adsorption and steric repulsionmechanism of polymers enables the formation of the metal nanoparticlesand ensures dispersion stability. In particular, very small metalnanoparticles are surrounded and adsorbed by the polymeric stabilizer toform clusters of the polymeric stabilizer-adsorbed metal nanoparticles.Since the clusters of the metal nanoparticles agglomerate, the metalnanoparticles forming the colloid appear to be much larger after theradioactive-rays irradiation. Accordingly, when the colloid of the metalnanoparticles is diluted and subjected to the ultrasonic treatment, theclusters of the metal nanoparticles are decomposed further into muchsmaller metal particles.

In the present invention, the much smaller particle diameter andnarrower distribution of particle diameters, compared to whenconventional methods are applied, are believed to be due to the use ofthe water-soluble polymeric stabilizer, such as polyvinyl pyrrolidone,(1-vinyl pyrrolidone)-acrylic acid copolymer, polyoxyethylene stearate,and (1-vinyl pyrrolidone)-vinyl acetic acid copolymer.

The metal nanoparticles having a very small diameter prepared in thepresent invention have a very large surface area-to-volume ratio, andthus they provide good antibacterial activity and conductivity even whenonly a trace is used. Therefore, the colloid solution of the metalnanoparticles according to the present invention can be used as anantibacterial agent, a sterilizer, a deodorizing agent, anelectromagnetic wave shielder, and conductive adhesive and ink.

For diversified industrial applications, the metal nanoparticlesaccording to the present invention need to be miscible with a variety oforganic solvents, plasticizers, and resins to prepare a non-aqueouscolloid solution of the metal nanoparticles. In this case, a non-aqueoussolvent, which does not contain water, i.e., an alcoholic solvent, canbe used alone as the solvent. The alcoholic solvent acts as a scavengeras well as the solvent, and thus is favorable for economical reasons.Among the above-listed kinds of alcoholic solvents, the ethylene glycolis more preferred as the solvent and scavenger.

For the miscibility with a variety of resins, plasticizers, andsolvents, instead of the ethylene glycol used as a non-aqueous alcohol,isopropyl alcohol can be used as the solvent and scavenger. In thiscase, the metal nanoparticles are miscible with alcohol-soluble resins,alcohol-soluble plasticizers, such as dioctyl phthalate (DOP), andorganic solvents.

In another aspect, the present invention provides a solid paste ofmetal-polymer nanocomposites. The solid paste of the metal-polymernanocomposites is prepared by a similar method as that applied toprepare the colloid solution of the metal nanoparticles as describedabove, except that polyacrylamide or polyethylene glycol is used as apolymeric stabilizer. The polyacrylamide and polyethylene glycol arewater-soluble polymers and precipitate the metal-polymer nanocompositeswhen dissolved in a solvent together with a metal salt, followed byradioactive-rays irradiation.

In the preparation of the solid paste of the metal-polymernanocomposites, when a water-insoluble stabilizer, such as poly(methyl(meth)acrylate), polyacrylonitrile, or polyurethane, is used, asurfactant, for example, polyoxyethylene sorbitan mono-oleate, which iscommercially available in the trade name of SPAN-80™, TWEEN-81™, orTWEEN-80™, is added. In this case, it is preferable to initially form anemulsion with the addition of the surfactant. The surfactant is addedlittle by little until the emulsion is formed.

As in the preparation of the colloid solution of the metalnanoparticles, in the preparation of the solid paste of themetal-polymer nanocomposites, it is preferable to use a mixture of waterand a non-aqueous solvent as the solvent, instead of using water or thenon-aqueous solvent alone.

In the preparation of the solid paste of the metal-polymernanocomposites, it is preferable that the metal salt is added in anamount of 0.01-5 parts by weight based on 100 parts of the solvent byweight. If the metal salt is added in an amount of less than 0.01 partsby weight, the effect of adding the metal salt is negligible. If themetal salt is added in an amount of greater than 5 parts by weight, theparticle size increases.

In the preparation of the metal-polymer nanocomposites according to thepresent invention, the polymeric stabilizer is added in an amount ofabout 0.1-10 parts by weight based on 100 parts of the solvent byweight. If the amount of the polymeric stabilizer is less than 0.1 partsby weight, the effect of adding the polymeric stabilizer is negligible.If the amount of the polymeric stabilizer exceeds 10 parts by weight,the particle size increases, and the addition of the polymericstabilizer such an amount is uneconomical.

In the preparation of the metal-polymer nanocomposites according to thepresent invention, the polymeric stabilizer and metal salt are dissolvedin a solvent, and a reaction container containing the solution is purgedwith nitrogen or argon gas for 30 minutes to 10 hours and completelytightened. Next, the solution is irradiated with gamma rays of aradiation dosage of about 10-50 KGy, followed by solvent removal andvacuum drying to attain the metal-polymer nanocomposites according tothe present invention.

The metal-polymer nanocomposites according to the present invention havea uniform particle diameter at room temperature. Since greatlydiversified kinds of polymers can be applied to the metal-polymernanocomposites, unlike conventional methods using monomers to preparemetal-polymer nanocomposites, it is easy to control the molecularweight. In addition, due to a great surface area-to-volume ratio of themetal-polymer nanocomposites, favorable effects, for example, in termsof antibacterial activity and conductivity, are provided with a trace ofthe metal-polymer nanocomposites. The metal-polymer nanocomposites canbe effectively used as an antibacterial agent, a sterilizer, adeodorizing agent, a conductive adhesive, and conductive ink.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 shows a transmission electron microscopic (TEM) photograph andparticle diameter distribution of silver nanoparticles prepared inExample 1 according to the present invention;

FIG. 2 shows the UV/VIS absorption spectrum of the silver nanoparticlesprepared in Example 1 according to the present invention at 405 nm;

FIG. 3 is a TEM photograph after dilution with water and ultrasonictreatment of the silver nanoparticles prepared in Example 2 according tothe present invention;

FIG. 4 shows a TEM photograph and particle diameter distribution ofsilver nanoparticles prepared in Example 5 according to the presentinvention;

FIG. 5 shows the UV/VIS absorption spectrum of the silver nanoparticlesprepared in Example 5 according to the present invention at 405 nm;

FIG. 6 is a field emission scanning electron microscopic (FESEM)photograph of a paste of silver-polymer nanocomposites prepared inExample 6 according to the present invention;

FIG. 7 shows a TEM photograph and particle diameter distribution of adispersion of silver-polymer nanocomposites prepared in Example 7according to the present invention in chloroform;

FIG. 8 shows the UVNIS absorption spectrum of the silver-polymernanocomposites prepared in Example 7 according to the present inventionat 405 nm;

FIG. 9 is a TEM photograph of a silver nanoparticle colloid solutionprepared in Example 1 according to the present invention after beingleft for 10 months at room temperature;

FIG. 10 shows the infrared (IR) spectrum of a silver nanoparticlecolloid solution prepared in Example 2 according to the presentinvention;

FIG. 11 shows the surface enhanced Raman scattering spectrum of thesilver nanoparticles prepared in Example 2 according to the presentinvention with respect to pH of a 1.0×10⁻⁵ M thionin solution; and

FIG. 12 shows the result of an antibacterial activity test of a textilesoaked with the silver nanoparticle colloid solution prepared in Example2 according to the present invention; and

FIG. 13 shows the result of an antibacterial activity test of a textilesoaked with a solution containing no silver nanoparticles according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in greater detail with referenceto the following examples. The following examples are for illustrativepurposes and are not intended to limit the scope of the invention.

EXAMPLE 1 Silver Nanoparticle Colloid Solution Prepared by Using(1-vinyl Pyrrolidone)-Acrylic Acid Copolymer as a Stabilizer

1.863 g AgNO₃, 395 g isopropyl alcohol, and 11.137 g (1-vinylpyrrolidone)-acrylic acid copolymer in a weight ratio of 75:25, having amolecular weight (MW) of 96,000, were thoroughly dissolved in 592 gwater. A reaction container containing the solution was purged withnitrogen gas for 1 hour and completely tightened, followed by gamma-raysradiation of a dosage of 30 KGy, thereby to prepare a yellow silvernanoparticle colloid solution.

Particle diameter distribution and particle shape were observed for theprepared silver nanoparticle colloid solution by using a transmissionelectron microscope (TEM). The results are shown in FIG. 1.

As shown in FIG. 1, the silver nanoparticle colloid solution had a veryuniform particle diameter distribution and a uniform particle shape.Most of the particles had a diameter of 3.0±0.9 nm on average, which isthe smallest among silver nanoparticles prepared by gamma-raysirradiation, which have been reported to date.

The formation of the silver nanoparticles was identified by UVNISspectrometry. The result is shown in FIG. 2. As shown in FIG. 2, anabsorption peak of the silver nanoparticles appeared at 405 nm.

EXAMPLE 2 Silver Nanoparticle Colloid Solution Prepared by UsingPolyvinyl Pyrrolidone as a Stabilizer

A silver nanoparticle colloid solution was prepared in the same manneras in Example 1, except that 11.137 g polyvinyl pyrrolidone having a MWof 55,000 was used as the stabilizer, instead of the (1-vinylpyrrolidone)-acrylic acid copolymer. The resultant silver nanoparticlecolloid solution had a minimum particle diameter of 6.6±1.1 nm and anaverage particle diameter of about 10-12 nm.

EXAMPLE 3 Silver Nanoparticle Colloid Solution Prepared by UsingPolyoxyethylene Stearate as a Stabilizer

A silver nanoparticle colloid solution was prepared in the same manneras in Example 1, except that 11.137 g polyoxyethylene stearate having aMW of ˜2,000 was used as the stabilizer, instead of the (1-vinylpyrrolidone)-acrylic acid copolymer. The resultant silver nanoparticlecolloid solution had an average particle diameter of 7.5±1.8 n m.

EXAMPLE 4 Particle Diameter of Silver Nanoparticle Colloid SolutionPrepared by Using Polyvinyl Pyrrolidone as a Stabilizer After Dilutionand Ultrasonic Treatment

The silver nanoparticle colloid solution (having an average particlediameter of 12.1±1.6 nm) prepared in Example 2 was diluted 20 folds withwater and subjected to ultrasonic treatment for 3 hours and particlediameter measurement. The result is shown in FIG. 3. As shown in FIG. 3,after the dilution and the ultrasonic treatment, particles of a diameterof ˜2 nm and ˜4 nm appeared. This result supports that the particlediameter can be further reduced by dilution and ultrasonic treatment.Apparently, a number of very small unit silver nanoparticles on whichpolyvinyl pyrrolidone is adsorbed form the silver nanoparticle colloidsolution.

EXAMPLE 5 Silver Nanoparticle Colloid Solution Prepared by UsingEthylene Glycol as a Solvent and Polyvinyl Pyrrolidone as a Stabilizer

A non-aqueous, yellow silver nanoparticle colloid solution was preparedin the same manner as in Example 1, except that 987 g ethylene glycolwas used, instead of the isopropyl alcohol and water.

Particle diameter and particle diameter distribution were observed forthe prepared silver nanoparticle colloid solution by using atransmission electron microscope (TEM). The results are shown in FIG. 4.As shown in FIG. 4, the silver nanoparticle colloid solution had a veryuniform particle diameter distribution and a small, uniform particlediameter of 6.02±0.8 nm on average.

The formation of the silver nanoparticles was identified by UV/VISspectrometry. The result is shown in FIG. 5. As shown in FIG. 5, anabsorption peak of the silver nanoparticles appeared at 405 nm.

EXAMPLE 6 Solid Paste of Silver-Polyacrylamide Nanocomposites Preparedby Using Polyacrylamide as a Stabilizer

592 g water, 1.863 g AgNO₃, and 395 g isopropyl alcohol were mixedtogether, and 11.137 g polyacrylamide was added to the mixture andvigorously stirred. A reaction container containing the solution waspurged with nitrogen gas for 1 hour and completely tightened, followedby gamma-rays radiation of a dosage of 30 KGy, thereby to attain a pasteof precipitates. The solvent was removed from the paste, followed byvacuum drying. As a result, silver-polyacrylamide nanocomposites wereobtained. The dried silver-polyacrylamide nanocomposites were dispersedin water.

The solid paste of the silver-polyacrylamide nanocomposites was observedby field emission scanning electron microscopy (FESEM). The result isshown in FIG. 6. As shown in FIG. 6, the silver-polyacrylamidenanocomposites had a particle diameter of 4-8 nm and a uniform particleshape.

EXAMPLE 7 Solid Paste of Silver-Poly(Methyl Methacrylate) NanocompositesPrepared by Using Poly(Methyl Methacrylate) as a Stabilizer

592 g water, 1.863 g AgNO₃, and 395 g isopropyl alcohol were mixedtogether, and 11.137 g poly(methyl methacrylate) was added to themixture and vigorously stirred. Twin-81 as a surfactant was added littleby little to the mixture with stirring until a white emulsion is formed.A reaction container containing the emulsion was purged with nitrogengas for 1 hour and completely tightened, followed by gamma-raysradiation of a dosage of 30 KGy, thereby to attain a solid paste ofprecipitates. The solvent was removed from the paste, followed by vacuumdrying. As a result, silver-poly(methyl methacrylate) nanocompositeswere obtained. The dried silver-poly(methyl methacrylate) nanocompositeswere dispersed in chloroform and subjected to TEM to observe the silverparticle diameter and shape. The result is shown in FIG. 7. As isapparent from the particle distribution of FIG. 7, the silver particleshad an average diameter of 6.55±1.27 nm and a uniform particle diameterand shape.

The formation of the silver-poly(methyl methacrylate) nanocomposites wasidentified by UVNIS spectrometry. The result is shown in FIG. 8. Asshown in FIG. 8, an absorption peak of the nanocomposites appeared at405 nm.

COMPARATIVE EXAMPLE

Among conventional silver nanoparticles prepared by gamma-rays radiationas in the present invention, silver nanoparticles prepared by usingsodium dodecyl sulfate as a stabilizer were reported to have a smallestparticle diameter of about 8 nm (Mater. Lett., 1993, 17, 314). In thisarticle, the silver nanoparticles had a considerably wide diameterdistribution ranging from 5 nm to 37 nm, having an average particlediameter of 13 nm.

Regarding silver-polymer nanocomposites, silver-poly(butylacrylate-co-styrene) nanocomposites prepared by gamma-rays irradiationof a water-in-oil emulsion were reported to have an average particlediameter of 8.5 nm (Chem. Commun. 1998, 941). In this article, theparticle diameter distribution was not apparent due to low magnificationof the TEM photograph.

EXPERIMENTAL EXAMPLE 1 Stability of Silver Nanoparticle Colloid Solution

To determine stability of the silver nanoparticle colloid solutionprepared in Example 1, the silver nanoparticle colloid solution was leftfor 10 months at room temperature and observed by TEM. The result isshown in FIG. 9. As shown in FIG. 9, the particle size was slightlyincreased, but the particle shape and the colloid state were stablymaintained without precipitation.

EXPERIMENTAL EXAMPLE 2 Interaction Between Silver and PolyvinylPyrrolidone

An Infrared (IR) spectrum was measured for the silver nanoparticlecolloid solution prepared in Example 2 to determine whether the silverand the polyvinyl pyrrolidone interact. The result is shown in FIG. 10.In FIG. 10, (a) is the IR spectrum for polyvinyl pyrrolidone alone, and(b) is the IR spectrum for the silver nanoparticles prepared in Example2 by using the polyvinyl pyrrolidone as a stabilizer. It is evident fromthe results of FIG. 10 that the silver and the polyvinyl pyrrolidoneinteract in the colloid solution.

EXPERIMENTAL EXAMPLE 3 Surface Enhanced Raman Scattering Measurement

Surface enhanced Raman scattering occurs in silver nanoparticle colloidsolutions. The Raman scattering spectrum of the silver nanoparticlesprepared in Example 2 was measured with respect to pH of a 1.0×10⁻⁵ Mthionin solution. The results are shown in FIG. 11. The results of FIG.11 show that the silver nanoparticles can be applied to surface enhancedRaman spectroscopy for assaying a trace of organic substances, includingbioorganic substances.

EXPERIMENTAL EXAMPLE 4 Antibacterial Activity Test in Textile

Antibacterial activity was measured in a textile soaked with the silvernanoparticle colloid solution prepared in Example 2, according to themethod of KS K 0693. The silver nanoparticle colloid solution of Example2 was diluted with water to 0.5%. 1.0%, and 1.5%, and textiles wereimmersed in each of the diluted sample solutions. Staphylococcus aureus(ATCC 6538) strain was used for the antibacterial activity test. Theresults for each of the samples are shown in Table 1 below. As shown inTable 1, the silver nanoparticle colloid solution according to thepresent invention showed a 99.9% antibacterial activity for all colloiddilutes.

TABLE 1 Antibacterial Activity Sample (% on average) 0.5% 99.9% 1.0%99.9% 1.5% 99.9%

In samples containing no silver nanoparticle colloid solution accordingto the present invention, white spots by the Staphylococcus aureus (ATCC6538) strain were observed, as shown in FIG. 13. In contrast, in thesamples containing the silver nanoparticle colloid solution according tothe present invention, the Staphylococcus aureus (ATCC 6538) strain washardly observed, as shown in FIG. 12.

According to the present invention, a metal nanoparticle colloidsolution and metal-polymer nanocomposites having a uniform particlediameter and shape can be prepared at room temperature on a large scale.Conventional methods using a reducing agent are ineffective to prepareuniform particles on a large scale. As is apparent from the observationby TEM, the metal nanoparticles according to the present invention havea more uniform, smaller particle diameter and shape, compared to metalnanoparticles that have been reported to date, and thus a great surfacearea to volume ratio. Therefore, the metal nanoparticle colloid solutionand metal-polymer nanocomposites according to the present invention havea high level of antibacterial activity even when only a trace is used.The metal nanoparticles according to the present invention have anano-scaled particle size and are greatly adsorptive due to polymersurrounding individual particles, and thus shows an effect of shieldingelectromagnetic waves when applied to the field of thin film coating, inaddition to antibacterial and sterilizing effects.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A method for preparing metal-polymernanocomposites, comprising: dissolving a metal salt and a polymericstabilizer in a solvent mixture of water and a non-aqueous solvent;purging a reaction container containing the solution with nitrogen orargon gas; and radiating radioactive rays onto the solution to obtainprecipitates, wherein said polymeric stabilizer is selected from thegroup consisting of polyethylene, polyacrylonitrile, poly(methyl(meth)acrylate), polyurethane, and polyethylene glycol.
 2. The method ofclaim 1, wherein the metal salt is a salt of at least one metal selectedfrom the group consisting of silver, copper, nickel, palladium, andplatinum.
 3. The method of claim 2, wherein the metal salt is a silversalt.
 4. The method of claim 3, wherein the silver salt is selected fromthe group consisting of silver nitrate, silver perchlorate, silversulfate, and silver acetate.
 5. The method of claim 1, wherein asurfactant is added to the solvent mixture of water and the non-aqueoussolvent together with the metal salt and the polymeric stabilizer toform an emulsion.
 6. The method of claim 5, wherein the surfactant ispolyoxyethylene sorbitan mono-oleate.
 7. The method of claim 1, whereinthe non-aqueous solvent is an alcoholic solvent.
 8. The method of claim7, wherein the alcoholic solvent is at least one selected from the groupconsisting of isopropyl alcohol, methanol, ethanol, and ethylene glycol.9. The method of claim 1, further comprising dilution and ultrasonictreatment after the formation of the precipitates.
 10. Metal-polymernanocomposites prepared by the method according to any one of claims 1through
 8. 11. A product comprising the metal-polymer nanocomposite ofclaim 1, wherein said product is selected from the group consisting ofan antibacterial agent, a sterilizer, a conductive adhesive, conductiveink, and an electromagnetic wave shielder for an image display.